Utilization of a complex comprising a titanium atom and organic ligands as a catalyst for asymmetric reactions has been widely known. Also known widely is the selection of an optically active compound, in particular an axially asymmetric hydroxylated compound, as an organic ligand of such complex.
It has been reported to select binaphthol as such hydroxylated compound and to utilize a titanium complex of this compound, i.e., a binaphthol-dichlorotitanium complex, as a catalyst for asymmetric synthesis (Mikami et al., J. Am. Chem. Soc., 1989, 111, 1940).
Although this complex is an excellent asymmetric catalyst, it still has problems that the stability thereof is slightly insufficient and the preparation thereof is somewhat troublesome.
In contrast, a binaphthol-diisopropoxytitanium complex can be prepared extremely easily, but has low catalytic activity. Use of the binaphthol-diisopropoxytitanium complex as an asymmetric catalyst is therefore impractical.
On the other hand, a technique has been reported in which a complex obtained by causing binaphthol to coordinate to a hydrolyzate of titanium isopropoxide represented by the chemical formula EQU (i-Pro-O).sub.2 Ti.dbd.O
(wherein i-Pro represents an isopropyl group) is used as an asymmetric catalyst (Mukaiyama et al., Chem. Lett., 1990, 1015).
The above asymmetric catalyst not only is insufficient in suitability for asymmetric reactions and in catalytic activity, but also has problems, for example, that the oxotitanium complex produced as an intermediate for the above complex catalyst is unstable and that the ligand exchange reaction tends not to proceed smoothly.